Esterase D, also known as ESD, is a serine hydrolase that belongs to the esterase D family. Esterase D is active toward numerous substrates including O-acetylated sialic acids, and it may be involved in the recycling of sialic acids. Esterase D gene is used as a genetic marker and a diagnostic tool for retinoblastoma, Wilson's disease and other hereditary or acquired diseases controlled by genes located at the 13 chromosome 13q14 region.